The present invention is particularly concerned with a breathing apparatus for divers of the type comprising a closed breathing circuit and a dosing bottle. In such apparatus, a dosing valve is adapted to alternately connect the dosing bottle to (i) a source of breathing gas for filling the dosing bottle or to (ii) the breathing circuit so that the contents of the dosing bottle is supplied to the breathing circuit. The breathing circuit characteristically comprises non-return valves for directing the gas flow in the breathing circuit as well as a container with a carbon dioxide absorbing substance, and a breathing bag.
A breathing apparatus of this kind is disclosed, for instance, in commonly assigned U.S. Pat. No. 4,031,887 (Botos et al). Apparatus of this type functions in such a way that a rebreathing takes place in the closed breathing circuit until the oxygen content of the breathing gas of the breathing circuit decreases to a predetermined value. Meanwhile, the dosing bottle is filled from a source of breathing gas. When the oxygen content decreases to the predetermined value, the breathing gas which has been stored in the dosing bottle is supplied to the breathing circuit at the same time as the used breathing gas is forced out to the surrounding medium. Thereafter, a new rebreathing period is started at the same time as the dosing bottle is refilled with breathing gas.